[petsc-dev] VecScatter problem

[Mark Adams]

So, this code works on lots of machines and the first scatter does work.

And it sounds like there is nothing wrong with this syntax, there is no
known race condition here.

Steve: are you using the debug version of PETSc that I built?

Note, this assignment:

  ! scatter solution back - apar
  apar = a_apar !!!! THIS ONE
  call VecCreateSeqWithArray(PETSC_COMM_SELF,ione,a_ts%nnode,apar,
xxvec(1),ierr);CHKERRQ(ierr)
  call VecScatterBegin(a_ts%from_petsc(1),a_XX,xxvec(1),INSERT_VALU
ES,SCATTER_FORWARD,ierr)

Is just so that any boundary conditions in nodes that PETSc does not touch,
get passed through this routine.

Steve: perhaps you could try setting apar = -1.d0, or something and look at
your plots to verify that it is not getting updated. Perhaps it is getting
updated with 0.0.  And now that I think about it, this assignment should
put some reasonable value in "apar" so if was not updated it should not be
zero.  Is that correct or could a_par be zero coming into this routine?

If need be I could add print statements in PETSc to dig into this.


On Thu, Aug 25, 2016 at 5:04 PM, Mark Adams <mfadams at lbl.gov> wrote:

> Matt is getting confused with Fortran, I just talked with him and he gets
> it now,
>
> On Thu, Aug 25, 2016 at 4:58 PM, Robert Hager <rhager at pppl.gov> wrote:
>
>> Now I am confused.  n1, which is a local variable in this subroutine, is
>> not declared as a pointer or as allocatable here, so there is memory
>> connected to n1. And in my understanding whatever values we get out of XX
>> with the VecScatter are written to this memory. After the scatter has
>> finished, we want those values to go into a_n1, which is an in/output of
>> this subroutine. That’s what the assignment a_n1=n1 does.
>>
>> Robert
>>
>>
>>
>> On Aug 25, 2016, at 3:56 PM, Matthew Knepley <knepley at gmail.com> wrote:
>>
>> On Thu, Aug 25, 2016 at 2:38 PM, Robert Hager <rhager at pppl.gov> wrote:
>>
>>> Isn’t xxvec(0) basically a pointer to n1 after the call to
>>> VecCreateSeqWithArray? If so, the VecScatter should update the values in n1
>>> and setting a_n1=n1 in the end makes sense.
>>>
>>
>> xxvec(0) holds a pointer (n1) to the data. That pointer does not change
>> when the scatter writes in to the Vec, so
>> at the end the pointer n1 is still the same, namely a_n1.
>>
>>    Matt
>>
>>
>>> Robert
>>>
>>>
>>>
>>> On Aug 25, 2016, at 3:16 PM, Matthew Knepley <knepley at gmail.com> wrote:
>>>
>>> On Thu, Aug 25, 2016 at 1:59 PM, Mark Adams <mfadams at lbl.gov> wrote:
>>>
>>>> We have the subroutine below that scatters three vectors.  We have used
>>>> this code on many machines and it works fine but on one machine data does
>>>> not get scattered correctly. The first scatter looks OK, but it looks like
>>>> the other two are missing data.
>>>>
>>>> Am I using this correctly?  Should we use VecGetArray in here instead
>>>> of just using the pointer used for construction? Is there a race condition
>>>> here that I'm missing?
>>>>
>>>> Thanks,
>>>> Mark
>>>>
>>>> subroutine scatter_to_xgc(a_ts,a_XX,a_n1,a_apar,a_phi,ierr)
>>>>   use petscts
>>>>   use sml_module,only:sml_mype
>>>>   use xgc_ts_module
>>>>   implicit none
>>>>   type(xgc_ts),intent(in)::a_ts
>>>>   Vec,intent(in)::a_XX
>>>>   real (kind=8),dimension(a_ts%nnode)::a_n1,a_apar,a_phi
>>>>   PetscErrorCode,intent(out)::ierr
>>>>   ! locals
>>>>   PetscInt,parameter::ione=1
>>>>   PetscScalar,dimension(a_ts%nnode)::n1,apar,phi
>>>>   Vec::xxvec(0:2)
>>>>
>>>>   ! scatter solution back - n1
>>>>   n1 = a_n1
>>>>
>>>
>>> Let me be clearer. Here n1 is equal to a_n1, and used to back xxvec(0).
>>> It does not change
>>> in the course of the function, so why would you have
>>>
>>>   a_n1 = n
>>>
>>> later on? What am I missing?
>>>
>>>    Matt
>>>
>>>
>>>>   call VecCreateSeqWithArray(PETSC_COMM_SELF,ione,a_ts%nnode,n1,xxv
>>>> ec(0),ierr);CHKERRQ(ierr)
>>>>   call VecScatterBegin(a_ts%from_petsc(0),a_XX,xxvec(0),INSERT_VALU
>>>> ES,SCATTER_FORWARD,ierr)
>>>>
>>>>   ! scatter solution back - apar
>>>>   apar = a_apar
>>>>   call VecCreateSeqWithArray(PETSC_COMM_SELF,ione,a_ts%nnode,apar,x
>>>> xvec(1),ierr);CHKERRQ(ierr)
>>>>   call VecScatterBegin(a_ts%from_petsc(1),a_XX,xxvec(1),INSERT_VALU
>>>> ES,SCATTER_FORWARD,ierr)
>>>>
>>>>   ! scatter solution back - phi
>>>>   phi = a_phi
>>>>   call VecCreateSeqWithArray(PETSC_COMM_SELF,ione,a_ts%nnode,phi,xx
>>>> vec(2),ierr);CHKERRQ(ierr)
>>>>   call VecScatterBegin(a_ts%from_petsc(2),a_XX,xxvec(2),INSERT_VALU
>>>> ES,SCATTER_FORWARD,ierr)
>>>>
>>>>   ! end
>>>>   call VecScatterEnd(  a_ts%from_petsc(0),a_XX,xxvec
>>>> (0),INSERT_VALUES,SCATTER_FORWARD,ierr)
>>>>   a_n1 = n1
>>>>   call VecDestroy(xxvec(0),ierr)
>>>>
>>>>   call VecScatterEnd(  a_ts%from_petsc(1),a_XX,xxvec
>>>> (1),INSERT_VALUES,SCATTER_FORWARD,ierr)
>>>>   a_apar = apar
>>>>   call VecDestroy(xxvec(1),ierr)
>>>>
>>>>   call VecScatterEnd(  a_ts%from_petsc(2),a_XX,xxvec
>>>> (2),INSERT_VALUES,SCATTER_FORWARD,ierr)
>>>>   a_phi = phi
>>>>   call VecDestroy(xxvec(2),ierr)
>>>>
>>>>   return
>>>> end subroutine scatter_to_xgc
>>>>
>>>
>>>
>>>
>>> --
>>> What most experimenters take for granted before they begin their
>>> experiments is infinitely more interesting than any results to which their
>>> experiments lead.
>>> -- Norbert Wiener
>>>
>>>
>>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>>
>>
>
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